In the wood industry it is of great importance to obtain precise measurements of the moisture content in the material to be processed, in order to achieve improved control of the process parameters. A precise knowledge of the relative amount of moisture content in the material is of a central importance for the quality of the end product in many processes within the wood and pulp industry. For example, it is advantageous to known in mechanical pulp processes whether the wood chips are fresh enough, i.e. having enough moisture content, to be able to be processable. Further, the optimal amount of chemicals to be added in the processes is dependent on the amount of fibers in the material, and in order to determine the amount of fibers it is necessary to correctly estimate the amount of moisture in the material.
Previously known methods to estimate the amount of fibers and moisture content in wood material involve drying of the material. However, such methods are cumbersome and tedious, and it would normally take a day or more until a correct measure value could be obtained, which delays the overall processing. It is therefore a need for a fast and reliable method to estimate the moisture content.
Similar needs exist in other industries handling biological material. For example, it would be advantageous to have a fast and reliable method for estimating the moisture content in the biological material in the bio energy field, in order to control the burning process more precisely, and improve its efficiency.
It is per se previously known to measure e.g. moisture content in wood using X-ray radiation. However, a common problem with such known methods is that that the apparatuses are large and expensive, that the methods are relatively tedious and cumbersome to perform, and/or that the results are imprecise and unreliable.
Further, the patent application WO 97/35175 by the same inventors discloses a method for using radiation of several energy levels in order to distinguish between e.g. different types of materials in wood, etc. However, this method requires additional measurement of the wood diameter, and is not adapted for e.g. moisture content estimations in automated processes.
Further, a very early example of use of X-ray for determining water-content in cellulosic sheets is disclosed in GB 1 115 904. However, the process discussed in this document is only to be used for thin sheets of material with known constituents, and is not suited for automatization. Still further, a paper titled “Measurement of moisture content in wood fuels with dual energy x-ray” by A. Nordell and K-J. Vikterlof, ISSN 0282-3772, discloses a similar approach for measuring moisture content in biofuels. However, also in this case the determination is based on prior knowledge of the material types and information related to this material type, and the process is neither intended nor suitable for an automated process.
There is therefore a need for a fast and accurate method and apparatus for estimating the moisture content in biological material, such as in wood, which can e.g. be used directly by people in field work operation, be used in automated processes, and the like.